Feb 28 (Reuters) - An avalanche of snow swept down a mountainside into a Missoula, Montana, neighborhood on Friday and engulfed a two-story house, injuring an 8-year-old boy and leaving two elderly people missing, police said.

The boy was pulled alive from the snow by rescue workers and volunteers digging with shovels more than an hour after the slide occurred, at about 4 p.m. local time (2300 GMT), but the two adults who lived at the home were believed to remain trapped, city police Sergeant Travis Welsh said.

The condition of the boy, who was taken to a nearby hospital, was not immediately known.

The avalanche occurred during a blizzard that forced the closure of the University of Montana campus and public schools in Missoula. Local authorities had warned earlier in the day of a heightened avalanche risk in the area, which lies at the foot of a mountain northeast of downtown.

Search and rescue teams were summoned to the area with special devices used to probe the snow for survivors. (Reporting by Laura Zuckerman in Salmon, Idaho; Writing by Steve Gorman; Editing by Cynthia Johnston and Lisa Shumaker)